This invention relates to polyvinyl butyral (PVB) resin and more particularly to (i) selectively cross-linked PVB, (ii) a plasticized sheet formed thereform and (iii) methods of forming such resin and sheet.
Plasticized PVB sheet is very well known as an intermediate for use with glass or plastic panels (hereinafter called "laminating panels") in laminated safety glass assemblies. It is also well known that the high temperature modulus properties of such a sheet and of the PVB resin from which it is made must be closely controlled for optimum performance. For example, if the resin is too stiff, the power required to melt and extrude it into sheet form may be excessive or the resulting sheet may be difficult to handle and may not provide a quality laminate during preparation of the safety glass assemblies. More specifically, when the sheet is too stiff, visually apparent, undesirable air bubbles can appear in the finished laminate. On the other hand, during lamination at the usual, relatively high (e.g. ca. 192.degree. C.) temperatures, it is important that the PVB flow adequately to collapse the sheet and fill the space between the two laminating panels, but not so much as to flow out the edges of the laminate which can occur if the modulus of the sheet is too low. In the past, such a delicate matching of the high temperature properties of the sheet to the laminating conditions has frequently not been possible with the result that the laminating operating conditions had to be inconveniently continuously adapted to the properties of the particular sheet being laminated. To the best of present knowledge, a means to control the high temperature properties of a plasticized PVB sheet has not been available in the past to one of ordinary skill in the art.